So-called push-type or continuous-heating furnaces are used for the heat treatment of billets, blocks and similar material of aluminum or aluminum alloys to be annealed, through which furnaces the material is moved and is thereby exposed to the annealing temperature of several hundred degrees.
The material is placed on crosshead shoes for its movement through the furnace. The crosshead shoes can be moved on rails of the furnace, for movement of which as a rule a hydraulic pushing device that can develop a pushing force of several hundred tons is utilized.
With long furnaces and thus long paths of movement for the heavily loaded crosshead shoes on the rails, significant problems exist for maintaining a lubricant supply for glide elements provided between the crosshead shoes and the rails in order to avoid wear of the glide elements. Problems also result from the fact that the rails and crosshead shoes shield the hot air flow circulated for the heat treatment from some parts of the material to be annealed, so that the areas of the material in the "lee" of the rails and crosshead shoes heat up slower.
Known designs try to solve the first-mentioned problem, for example by using as the lubricant a graphite-oil mixture of a dry, powdery graphite lubricant, which is applied to the rails from a storage chamber of the crosshead shoe when the crosshead shoe is placed onto the rails. This measure, however, is complicated during the practical operation and as a rule is only effective at the start of the movement. After only a few meters, the remainder of the path must be covered in a dry operation using much power and with much resulting wear of the glide surfaces.
It is also known to achieve an improved sliding capability with glide elements such as a glide bar or glide plates which are made of a colloidal graphite and are mounted on the underside of the crosshead shoe surface or on the rail. However, these glide elements cannot sufficiently withstand high loads. In particular, at the corners and edges, parts of the glide elements will break off, so that the glide surfaces are significantly damaged by broken pieces, rough broken edges and wear, and thus no longer fulfill their function as a "glide surface". Also, edges are dangerous which are arranged perpendicular to the direction of movement on the glide surfaces. In other attempts to reduce wear and keep broken pieces away from the glide surface, grooves which are inclined with respect to the direction of movement have been provided in rectangular glide plates. This measure, however, is hardly successful, because the inclined grooves in the rectangular glide plates result in angles under 90.degree., which makes the plates very susceptible to pieces breaking off. Furthermore, larger broken pieces can get caught in the grooves and thus can result in further destruction of the glide surface. Damaged or even destroyed glide elements result in a great resistance to movement, so that large forces are required in order to move the crosshead shoe with the material being annealed.
Significantly smaller forces for moving the crosshead shoes with the annealing material supported thereon are needed in the conveying device known from Swiss Patent No. 666 117, in which the crosshead shoe is supported on the rails by a continuous roller conveyor extending in the conveying direction. However, this solution is very complicated in its construction and is expensive both to manufacture and also to service.
A purpose of the present invention is to provide a conveying device of this type which avoids the disadvantages of the conventional constructions while providing movement between the crosshead shoes and the rails which is as wear-resistant and jerk-resistant as possible, and at the same time permitting a pairing of glide elements on the crosshead shoes and rails with a low friction coefficient.